1. Field of the Invention
This invention relates to a process for the preparation of sodium percarbonate or sodium perborate having a good flowability and a high specific volume.
2. Description of the Prior Art
Sodium perborate (NaBO.sub.2.H.sub.2 O.sub.2.3H.sub.2 O) has an excellent stability and it has been used for a long time as a powdery bleaching agent in Europe and America. However, because the bleaching effect of this compound is insufficient at lower temperatures, in Japan, where washing is conducted by using cold water, sodium perborate is not very suitable as a bleaching agent and it is scarcely used. Sodium percarbonate (Na.sub.2 CO.sub.3.3/2 H.sub.2 O.sub.2) has a higher water solubility than sodium perborate and it has the advantage that it readily dissolves in cold water. Accordingly, this bleaching agent is widely used in Japan.
A conventional bleaching detergent composition comprises a powdery detergent having incorporated therein from 10 to 20 wt.% of sodium percarbonate or sodium perborate. However, when such a bleaching agent is incorporated in a detergent, because of the differences of the specific volumes, the shapes and the particle sizes of the two components, due to the shaking and vibration that occurs during transportation, the sodium percarbonate or sodium perborate becomes concentrated in the central portion of the package. Namely, a classification phenomenon occurs. Because of this classification phenomenon, the distribution of the bleaching agent in the detergent composition becomes non-uniform and attainment of a uniform bleaching effect of the bleaching agent cannot be expected. Further, these peroxides are defective in that they are inferior in flowability in the powder state and caking readily occurs during storage.
Various methods have heretofore been proposed as means for minimizing or overcoming these difficulties or disadvantages. For example, there can be mentioned a method comprising mixing a peroxide, such as sodium percarbonate, with water and granulating and drying the mixture; a method comprising agitating and fluidizing a peroxide in an inert organic solvent such as carbon tetrachloride and drying the thus-treated peroxide; a method comprising using sodium chloride as a nucleus during precipitation of the peroxide; and a method comprising adding water to a molten peroxide, agitating the mixture, incorporating a powder of the same peroxide into the agitated mixture, and cooling the mixture under agitation. According to these known methods, however, it is impossible to obtain a powdery bleaching agent having an excellent flowability and a high specific volume.